Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known foil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
In many cases, accessory components are attached to the rotor blades of wind turbines to perform various functions during operation of the wind turbine. For example, it is known to change the aerodynamic characteristics of wind turbine rotor blades by adding protrusions or other structures (often referred to as “vortex generators”) to the surface of the blade in order to increase the energy conversion efficiency during normal operation of the wind turbine by increasing the lift force of the blades while decreasing the drag force. Vortex generators serve to increase the attached-flow region and to reduce the detached-flow region by moving the point of flow separation nearer to the trailing edge of the blade or to delay it from occurring altogether. In particular, vortex generators create local regions of longitudinally rotating, turbulent airflow over the surface of the blade as a means to delay flow separation and thus optimize aerodynamic airflow around the blade contour.
Laminar boundary layer instability noise occurs, however, when flow instabilities are scattered by a uniform discontinuity (e.g. the edge of a vortex generator panel or other blade add-on component) on the rotor blade surface. These scattered acoustic waves travel upstream, where they interact with and amplify the initial amplitude of the flow instabilities. The result is a feedback loop that produces multiple acoustic tones, regularly-spaced in frequency, which create undesirable noise for the wind turbine.
Thus, an improved vortex generator or blade add-on that addresses the aforementioned issues would be advantageous. Specifically, vortex generators for wind turbine rotor blades having noise-reducing features would be desired.